include/asm-mips/timex.h

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 1998, 1999, 2003 by Ralf Baechle
   7  */
   8 #ifndef _ASM_TIMEX_H
   9 #define _ASM_TIMEX_H
  10
  11 #ifdef __KERNEL__
  12
  13 #include <asm/mipsregs.h>
  14
  15 /*
  16  * This is the frequency of the timer used for Linux's timer interrupt.
  17  * The value should be defined as accurate as possible or under certain
  18  * circumstances Linux timekeeping might become inaccurate or fail.
  19  *
  20  * For many system the exact clockrate of the timer isn't known but due to
  21  * the way this value is used we can get away with a wrong value as long
  22  * as this value is:
  23  *
  24  *  - a multiple of HZ
  25  *  - a divisor of the actual rate
  26  *
  27  * 500000 is a good such cheat value.
  28  *
  29  * The obscure number 1193182 is the same as used by the original i8254
  30  * time in legacy PC hardware; the chip unfortunately also found in a
  31  * bunch of MIPS systems.  The last remaining user of the i8254 for the
  32  * timer interrupt is the RM200; it's a very standard system so there is
  33  * no reason to make this a separate architecture.
  34  */
  35
  36 #include <timex.h>
  37
  38 /*
  39  * Standard way to access the cycle counter.
  40  * Currently only used on SMP for scheduling.
  41  *
  42  * Only the low 32 bits are available as a continuously counting entity.
  43  * But this only means we'll force a reschedule every 8 seconds or so,
  44  * which isn't an evil thing.
  45  *
  46  * We know that all SMP capable CPUs have cycle counters.
  47  */
  48
  49 typedef unsigned int cycles_t;
  50
  51 static inline cycles_t get_cycles (void)
  52 {
  53         return read_c0_count();
  54 }
  55
  56 #endif /* __KERNEL__ */
  57
  58 #endif /*  _ASM_TIMEX_H */